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93c19634f7
The CPER ring debugfs read code always writes a 12-byte header when the
file is read for the first time (*offset == 0):
copy_to_user(buf, ring_header, 12);
But the code never checks whether the user buffer (@size) is at least
12 bytes long. After writing the 12-byte header, the code then gives the
full original @size to the CPER payload handler:
record_req->buf_size = size;
This means the function can write:
12 bytes (header) + payload bytes (up to @size)
into a buffer that is only @size bytes big. In other words, the kernel
may write more data than the user asked for. This can overflow the user
buffer.
The fix is:
- If the user buffer is smaller than 12 bytes on the first read,
return -EINVAL instead of copying the header.
- After writing the 12-byte header, subtract 12 from @size and pass
the reduced size to record_req->buf_size. This ensures the CPER
payload only uses the remaining free space in the buffer.
Reads after the first one (*offset != 0) do not write the header, so
their behavior stays exactly the same. The only user-visible change is
that tiny buffers now fail safely instead of risking an overflow.
Fixes:
drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:523
amdgpu_ras_cper_debugfs_read()
warn: userbuf overflow? is 'ring_header_size' <= 'size'
Fixes:
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.